Sinclair ZX80 / ZX81 / Z88 Forums

I have just got a zeddy and it is a bit poorly. I believe the ULA is dead amongst other things - I put the ULA in a known working zeddy and it produces a white screen with no cursor.

Having put in a working ULA I get the following:-
I have done the following so far:-

Swapped out the ULA (to get the cursor)
Swapped the Z80
Swapped the ROM
Plugged in a 16k RAM pack to bypass the onboard RAM

The PCB is in lovely condition:-


Could it be the modulator? I haven't had time to fit a ZX8-CCB yet.

Any further suggestions? I don't have a 'scope or anything that sophisticated!

Also there is some of the keyboard strip stuck in the KB2 connector - not me being clumsy! The ribbon was already broken when I opened it. Any suggestions as to how best to remove it without destroying the contacts?

Thanks

Lardo

The modulator might have a tiny tuning pot - you could wiggle that. That pattern also kind-of reminds me of a power issue I once had. Do they move or are they static?

I have had black banding albeit horizontal when the power supply or regulator is giving up the ghost so assuming a good power pack the only thing I can suggest,Lardo is to multi meter the regulator and check for a steady 5volts, taking care not short anything.

As for the broken ribbon try using two jewellers screwdrivers of the smallest size if you posses them in a pincer like fashion to tease the cable up taking care not to damage the contacts.

sirmorris wrote: ↑Thu Jun 08, 2017 3:24 pm The modulator might have a tiny tuning pot - you could wiggle that. That pattern also kind-of reminds me of a power issue I once had. Do they move or are they static?

They are pretty static - I am using a good quality power pack and will replace the regulator with a new one.

I have never wiggled the modulator before! Very liberating. I tried various setting and after re-tuning the telly got this:-


It is an early ULA I am using so a black output is not unexpected I guess. Maybe a combination of composite mod and new regulator will sort it. I will find out when I have time to dust off the soldering iron!

I also need to find out where I can buy a reasonably priced ULA! If there is such a thing these days.

Lardo

Moggy wrote: ↑Thu Jun 08, 2017 3:26 pm I have had black banding albeit horizontal when the power supply or regulator is giving up the ghost so assuming a good power pack the only thing I can suggest,Lardo is to multi meter the regulator and check for a steady 5volts, taking care not short anything.

As for the broken ribbon try using two jewellers screwdrivers of the smallest size if you posses them in a pincer like fashion to tease the cable up taking care not to damage the contacts.

I have a set of jewellers screw drivers so will give it a go. I managed to do similar before (my fault that time) and stuffed up the connector in the process - I bent one of the contractors back. Had the replace the whole connector which was a pain.

Edit - removed the last remaining bit with no damage!

Lardo Boffin wrote: ↑Thu Jun 08, 2017 3:55 pm
I also need to find out where I can buy a reasonably priced ULA! If there is such a thing these days.

Lardo

You can try here: viewtopic.php?f=8&t=2386
Not sure if these are already sold, but you could give it a try!

MaFli wrote: ↑Thu Jun 08, 2017 4:08 pm

Lardo Boffin wrote: ↑Thu Jun 08, 2017 3:55 pm
I also need to find out where I can buy a reasonably priced ULA! If there is such a thing these days.

Lardo

You can try here: viewtopic.php?f=8&t=2386
Not sure if these are already sold, but you could give it a try!

Thanks. I had seen those a while ago but at £28 each I was hoping to find something a little cheaper if possible!

£28 each is far too expensive, especially as they are not fully tested and seller wont give refund if found partly duff..

your machine has the earliest ula and this is lacking the 'back porch' part of the signal, so WILL give poor dark picture on a colour tv, even if its perfectly ok... it will usually be ok on a black & white set..the zxvid or zxccb will cure it by adding the back porch..dont worry too much about the 'bands' at the moment, they will most likely also disappear with a zxvid /zxccb

Having fitted a ZX8-CCB all is well. I now need to tune it in properly and find a replacement ULA.